The present application relates generally to automated material handling systems, and more specifically to an automated material handling system including an improved extractor/buffer apparatus that provides a highly efficient interface between storage locations and transport equipment for Work-In-Process (WIP) parts.
Automated material handling systems are known that employ WIP storage units and transport equipment to store WIP parts and to move them between workstations and/or processing machines in a product manufacturing environment. For example, such an automated material handling system may be employed in the fabrication of Integrated Circuit (IC) chips. A typical process of fabricating IC chips includes various processing steps such as deposition, cleaning, ion implantation, etching, and passivation steps. Each of these steps in the IC chip fabrication process may be performed by a different processing machine such as a chemical vapor deposition chamber, an ion implantation chamber, or an etcher. Further, the WIP parts, in this case, semiconductor wafers, are typically moved between the different workstations and/or processing machines multiple times to perform the various steps required for fabricating the IC chips.
A conventional automated material handling system used in an IC chip fabrication process comprises a plurality of WIP storage units for storing semiconductor wafers, and transport equipment including overhead hoists and conveyors for moving the wafers between the storage units, workstations, and processing machines on the IC chip manufacturing floor. The wafers are typically loaded into carriers such as Front Opening Unified Pods (FOUPs), each of which may be selectively accessed via an overhead hoist traveling on a suspended track. In a typical system configuration, the FOUPs are accessed by overhead hoists from locations underneath the track. Accordingly, each overhead hoist is typically moved along the suspended track to a position directly above a selected location, lowered toward the selected location, and operated to pick/place a FOUP from/to that location.
In the conventional automated material handling system, overhead hoists are employed to move FOUPs relatively short distances while conveyors are employed to move the FOUPs longer distances across the IC chip manufacturing floor. For example, a conveyor used in an IC chip manufacturing environment may comprise a conveyor belt, or a platform configured to travel along a rail. In the typical system configuration, overhead hoists may be employed to pick/place respective FOUPs from/to one or more conveyors. The overhead hoists may also be used to pick respective FOUPs from the conveyors and to place the FOUPs to input/output ports of a workstation or processing machine, and vice versa. The overhead hoists typically access the FOUPs from the conveyors positioned underneath the suspended track.
One drawback of the above-described conventional automated material handling system is that each overhead hoist employed therein typically picks/places only one FOUP at a time. This can significantly impede throughput in a system capable of handling hundreds of FOUPs. Further, each overhead hoist typically accesses just a single level of storage underneath the suspended track. This is also problematic because providing only one level of WIP storage on the product manufacturing floor can increase costs due to the inefficient use of floor space. To access multiple levels of storage underneath the track, storage units must typically be configured to move a selected FOUP from its current position within the storage unit to a position at the level accessible to the overhead hoist, thereby further impeding the system throughput. In addition, such storage units typically have many moving parts such as rollers, bearings, and motors that are subject to failure, which not only increases costs but also diminishes the reliability of the overall system.
Moreover, because the overhead hoists are typically configured to access FOUPs from locations underneath the suspended track, a minimum amount of space is required between the ceiling and floor of the IC chip manufacturing facility to accommodate the track and the overhead hoist. This further limits the amount of space in the manufacturing facility that might otherwise be used for storing semiconductor wafers. In addition, because only one level of storage is accessible to each overhead hoist, multiple overhead hoists must normally queue up at a storage unit to access FOUPs from that storage unit, thereby further lowering system throughput.
It would therefore be desirable to have an automated material handling system that provides enhanced material handling efficiency while overcoming the drawbacks of conventional automated material handling systems.